This relates to a battery housing made from an intumescent flame retardant material that intumesces in the event of a thermal runaway of a housed battery.
Batteries have long been used as mobile power sources. In recent years, advancements have increased the power density of both primary (non-rechargeable) and secondary (rechargeable) batteries. For example, the power density of primary lithium batteries has reached 4.32 MJ/L, while the power density of secondary lithium ion batteries has reached 2.63 MJ/L. As a result, the use of lithium and lithium ion batteries has become wide spread in a variety of applications, including consumer electronics, medical devices, industrial equipment, and hybrid/electric automobiles.
However, many batteries, and particularly lithium and lithium ion batteries, are vulnerable to thermal runaways, during which heat and gas are rapidly discharged from a battery and a fire hazard is created. A thermal runaway may be caused by manufacturing defects, accumulation of heat, internal short circuits, or external impacts or trauma. Further, a thermal runaway of a single battery may trigger the thermal runaway of adjacent batteries, and thereby cause a dangerous chain reaction.
It is known to apply a fire-resistant coating to batteries or to enclose batteries within fire-resistant walls. However, a fire-resistant coating or wall often does not provide sufficient thermal insulation to prevent a thermal runaway from causing further thermal runaways of other batteries kept in close proximity. In fact, some fire-resistant materials used for coatings or walls, such as mica, have relatively high thermal conductivity. It is also known to apply an intumescent coating to batteries. However, intumescent coatings typically cannot be applied in a layer thick enough to overcome the drawbacks mentioned above. In any event, applying a coating introduces an additional manufacturing step. Further, the functionality of a coating may be compromised by scratching or peeling.